Printing systems such as copiers, printers, facsimile devices or other systems having a print engine for creating visual images, graphics, texts, etc. on a page or other printable medium typically include various media feeding and sensing systems for introducing original image media or printable media into the system and monitoring the media as it traverses a media path. Examples include thermal transfer printers. Typically, a thermal transfer printer is a printer which prints on media by melting a coating of ribbon so that it stays glued to the media on which the print is applied. It contrasts with direct thermal printing where no ribbon is present in the process. Typically, thermal transfer printers comprise a supply spindle operable for supplying a media web and ribbon, a print station, and a take up spindle. New ribbon and media is fed from the supply spindle to the print station for printing and then the ribbon is wound up by the take up spindle while the media is exited from the print station. The media path typically includes a top-of-form (top of label) sensor operable for sensing holes or notches in the media, locating a leading edge or gap located on the media, or reading black marks on either the top or bottom of the media.
Thermal transfer printers typically provide two ways in which to locate the top-of-form of certain media. Conventional methods and apparatus for such location is dependent upon the type of media or label being printed on. Most labels have a ⅛th inch gap between each label. In these cases, the printer typically utilizes a transmissive or gap sensor located adjacent the entrance of the printhead along the media feed path. This sensor shines a light at the label while another sensor measures how much light is getting through. More light gets though the gap between labels letting the printer know where the top-of-form is. The same type of sensor works when the media type includes holes or notches on one side.
The second type of sensor that may be relied upon by conventional devices is a reflective or mark sensor. This type of sensor is used for media that has a black line on the back. Instead of shining light through the label it shines light on the bottom of the media and monitors how much light is reflected back. When the light hits the black line the light level changes, letting the printer know where the top-of-form is.
Undesirably, current top of form sensing apparatus and methods do not provide for versatility in the media type used. It would, therefore, be desirable to provide a sensor operable for sensing holes or notches in media, locating a leading edge or gap located on media, and reading black marks or other symbols on either the top or bottom of media. It would further be desirable to provide a sensor having a resolution of sensor locations that is fine enough such that the overall sensor assembly can be fixed in single location requiring no adjustments. Still further, it would be desirable to provide a top-of-form sensor can easily be removed or installed in a printer for cleaning and maintenance.